JNI data types

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JNI data types

JNI overhead

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In our initial JNI example, we declared a Java method that took an int parameter and saw that the resulting C function generated by the javah tool took (along with a couple of other parameters) a parameter of type jint. In fact, the Java method also returned an int, and the corresponding C method a jint. Here are the two side by side as a reminder:

Java:	public native static int getDoubled(int n);
C:	JNIEXPORT jint JNICALL Java_test_Test_getDoubled(JNIEnv , jclass, jint*);

From this example, you'll hopefully be unsurprised to learn that for each Java primitive type, there is a corresponding C type declared in the JNI headers. So a Java boolean becomes a C jboolean, a Java char a C jchar etc:

Java primitive type	Corresponding C type with JNI	Bytes
boolean	jboolean	1
byte	jbyte	1
char	jchar	2 (unsigned)
short	jshort	2 (signed)
int	jint	4
long	jlong	8
float	jfloat	4
double	jdouble	8